LB 27-227 - A pairwise competition experiment reveals the role of soil microbiomes in plant invasion

Conservation and restoration of the remnant native prairies in Northern America are critical in protecting these ecosystems and preserving their biodiversity. The rapid spread of invasive plant species, however, has caused many native grassland ecosystems to be outcompeted entirely, resulting in an overall homogenization of ecosystems. Global estimates suggest that most grasslands will experience increased atmospheric nitrogen deposition by 2030. Native species might lose their natural competitive ability under varying nitrogen levels, with subsequent declines in grassland diversity. Plant–soil feedback can explain how exotic plant species invade and alter ecosystem functioning. Plant species differentially alter soil communities by cultivating a microbiota specific to each species. Despite the critical role of plant-soil feedback in invasion dynamics, our understanding remains limited. Here we conducted a greenhouse experiment to study the pairwise interactions under three different soil nitrogen levels. Specifically, our goal was to understand whether the invasive and native species influence microbiota differently by examining the structure and composition of rhizosphere microbial communities of invasive species grown with native grasses under different nitrogen regimes at different time points. We selected an invasive cool-season C3 grass species (Kentucky bluegrass), a functionally similar cool-season C3 grass species (Western wheatgrass), and another functionally dissimilar native warm season C4 grass (blue grama). Then, using quantitative PCR and Illumina MiSeq sequencing of bacterial 16S rRNA and fungal ITS genes, we interrogated microbial abundance and community structure, respectively. Results of quantitative PCR revealed significant differences in bacterial 16S rRNA copy numbers across nitrogen levels and species interactions. However, fungal ITS copy numbers significantly differed across nitrogen levels but not species interactions. Fungal ITS copy numbers were significantly different across nitrogen levels but not species interactions. Principal coordinate analysis (PCoA) showed distinct microbial groups while PERMANOVA confirmed the significant effects of time and nitrogen levels on microbial community structure. Overall, this study reveals how invasive plants modify soil microbial communities to outcompete their native counterparts.